Styrbjorn took in Eivor as a child, after her father's murder at the hands of Kjotve the Cruel. Styrbjorn then raised her as his own, alongside his own son Sigurd. After a time, Styrbjorn had grown weary of the constant fighting and grabs for power. In 872, Styrbjorn made an alliance with Harald Fairhair, he who would be the first king of a unified Norway, and in the process surrendered his lands and title to the would-be-king. Such a move however angered his son, believing his title stolen from him, and thus a rift formed between the father and son.
Styrbjorn was the son of Sigvaldi, a jarl of Stavanger. Upon Sigvaldi's death, Styrbjorn took lordship over the region. After Eivor lost her parents Varin and Rosta at the age of nine, Styrbjorn adopted and raised her as his own alongside his son, Sigurd.
Misfortune of Gull
When Eivor had grown, she returned home one day with her clanmates Tora Auzoux and Dag Nithisson from preventing a raid on a village in Rygjafylke by Kjotve the Cruel, having hoped that by saving the settlement, it would convince the population to swear allegiance to their father. However, Styrbjorn chastised Eivor's actions in bringing Kjotve's tattooed slave, a woman named Gull, back to Stavanger as a prize, saying that her presence would bring disaster and death.
Such backlash drew the ire of his adopted daughter, who vented her frustrations elsewhere. Styrbjorn's warning later came true, as Fornburg was later attacked by the Wolf Clan. Felling the jarl with two arrows into his back. He was helped up by Tora who attempted to get him to safety, though the king was intent on staying and fighting, cursing what Eivor had brought upon them and demanding her whereabouts. As the fighting continued, Tora was killed before Eivor arrived and saved what was left of the clan. All together, they managed to stop the advancement of the Wolf Clan.
Alliance with Harald and later years
In 872, Styrbjorn saw fit to gift Sigurd's birthright of land without his knowledge or consent as a pledge of fealty to Harald Fairhair, a contender for the kingship of a united Norway torn by resource strain and endless war. This drove a wedge between father and son, and coupled with what Sigurd had learned from the Hidden One Basim Ibn Ishaq on his two-year journey to Constantinople, was the final straw in driving him to leave Norway with Eivor and select members of the Raven Clan in search of better prospects among the many kingdoms of the nearby England.
By 877, Styrbjorn was little more than a stumbling drunk, spending his days at the local tavern of Alrekstad and his nights on barren planks of wood. He also bathed little, and was the butt of many comments regarding this. One winter's day, he was surprised by the arrival of Sigurd and Eivor. Immediately rising from his stupor, Styrbjorn sobered up and greeted the two. His son, however, was unhappy to so see him, still mad about his father's surrender. Styrbjorn, upon noticing Sigurd's missing arm expressed deep concern at his well-being, although he was pushed away.
Styrbjorn surmised that they had returned to make another war against King Harald, though Sigurd wanted nothing to do with what he thought of as nothing more than a "frozen backwater". Styrbjorn had always hoped at his son's return, but Sigurd no longer held any aspirations of kingship, believing his destiny laying elsewhere. Styrbjorn stood as his son mocked him for his failure, forfeiting his birthright. The former jarl shot back that Sigurd was never home, therefore never interested in ruling to begin with. When Sigurd tried to defend the comment, that he was spreading the word of his father, Styrbjorn raised his voice that the people of Constantinople had no need for his name. Sigurd, more angered than before left, leaving Styrbjorn and Eivor as they expressed their farewells.
Personality and traits
Styrbjorn was, at heart, a very considerate and wise ruler who wished nothing but the best for his people. He reprimanded Sigurd and Eivor for their hasty approach in dealing Kjotve that nearly cost the two their lives and even cited that he worked on securing alliance to improve the odds against their enemy's forces, showing that he would not condone recklessness. Yet, it became evident to Sigurd and Eivor that Styrbjorn had since disillusioned by their culture's pursuit for honor and glory through battles stemmed from constant infighting between the Norse clans, an issue that came to light during the unification of Norway where he reluctantly swore fealty to King Harald in addition of not disparaging Varin's sacrifice as a cowardly act. Thought that costed him greatly with his children painted him as selfish, Styrbjorn made it clear that he didn't regret his decision as his people at very least lived on despite of them ended up became part of Harald's subjects in the united Norway, showing the extent of his willingness to preserve lives and choosing between lesser of two evils. 
Behind the scenes
In issue #1 of Valhalla's prequel comic series Song of Glory, Styrbjorn's father is named as Olaf. While in The Art of Assassin's Creed: Valhalla, his father is named Harald. Both of these conflict with the ship story about Nal told by Bragi while aboard Eivor's personal longship, where Bragi instead names a "Sigvaldi" as Styrbjorn's father.
- Assassin's Creed Valhalla: Song of Glory (first appearance)
- Assassin's Creed: Valhalla
- Assassin's Creed: Rebellion – The Ravens' Wound (mentioned only)
- Assassin's Creed Valhalla: Geirmund's Saga
- Assassin's Creed: Valhalla – Floating conversations: Ship stories
- Assassin's Creed Valhalla: Song of Glory – Issue #01
- Assassin's Creed: Valhalla – Prologue
- Assassin's Creed: Valhalla – Honor Bound
- Assassin's Creed Valhalla: Song of Glory – Issue #02
- Assassin's Creed Valhalla: Song of Glory – Issue #03
- Assassin's Creed: Valhalla – Birthrights
- Assassin's Creed: Valhalla – The Prodigal Prince
- Assassin's Creed: Valhalla – Where Legends Are Born
- Assassin's Creed: Valhalla – The Seas of Fate